Description of Pneumatic Controllers
Pneumatics is a branch of mechanical engineering that uses compressed air for power. When air is squeezed into a small space, the pressure it exerts on the sides of its container increases. This allows compressed air tools to perform work, just like hydraulic or electric tools. Pneumatics are used to power motors, lifts, nail guns and drills.. Pneumatic controllers are also powered by compressed air, and are used to regulate pneumatic systems.
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History
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The oldest form of pneumatic device is the bellows, a primitive air compressor. Pneumatics started developing as a serious science in the seventeenth century, with the development of the first efficient air compressors. However, it was not until the twentieth century that pneumatic engineering became well-developed enough to produce pneumatic controllers. In the late 1960s, digital logic-based pneumatic controllers were invented and applied to industrial pneumatics.
Uses
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Pneumatic controllers can perform any task that electric controllers can. They can serve as pressure switches, turning a system on or off if the pressure rises (or falls) to a preset limit. They can function as time switches, turning a system on or off after a certain amount of time has elapsed. They can even work as counters, recording the number of times a certain event has happened.
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Benefits
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Pneumatic controllers are particularly useful in environments with high levels of dust in the air, or high levels of humidity. Moisture and dust can easily damage electric controls but have little effect on pneumatic controls. Pneumatic controllers use no toxic chemicals, and so present no danger if they develop leaks. Pneumatic controllers present no risk of causing electric shocks, explosions, or fires. If a fire starts elsewhere and spreads to a pneumatic control system, the controllers are not flammable and so cannot add to the fire. They are ideal for hazardous industrial conditions.
Drawbacks
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Pneumatic controllers have a few drawbacks as well. There are not many experts available that know how to troubleshoot and repair them. Pneumatic controller air conduction lines that are longer than 10 to 15 feet can take longer to respond than electric circuits. Additionally, poor air quality may shorten the lives of pneumatic controllers.
Types
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Pneumatic controllers are miniature 3-way or 4-way valves. These valves open to turn on a pneumatic system and close to turn it off. “And” controllers only open the output valve if both of their input valves are receiving air signals. If either input valve of an “Or” element is receiving a signal, then its output valve opens. A “Not” element shuts off its output if its input receives a signal and opens it if its input has no signal. “Memory” elements keep their last position even without an air supply. “Time-on” and “Time-off” elements open or close systems after a certain amount of time has lapsed. More complex pneumatic controllers can be built by combining multiple basic elements.
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